In one aspect, this invention relates to aqueous polymeric dispersions and to their use as the binder component of aqueous pigmented coating compositions. In another aspect, this invention relates to aqueous paper coating compositions and to coated paper articles made therewith.
In the paper industry, various types of paper sheets or substrates are coated with pigmented paper coating compositions in order to modify various characteristics thereof (e.g., surface smoothness and gloss, printability, ink receptivity, stiffness, opacity, etc.). In such coating operations, an aqueous coating composition containing an adhesive component (commonly called a binder) and a pigment is applied to one or both surfaces of the paper substrate by various techniques such as by the use of a blade coater, an air knife, roll coater, rod coater and the like.
Many different types of binder components have been suggested in the prior art for use in the aforementioned paper coating compositions. Such binder components have included natural materials such as starch, casein, soy bean protein, etc.; synthetic polymeric materials such as emulsions or latexes of carboxylated styrene/butadiene copolymers, latexes of copolymers of esters of acrylic and/or methacrylic acid, aqueous solutions of certain water- or alkali-soluble synthetic polymers, etc.; and combinations thereof. However, such prior art binder components typically suffer from one or more deficiencies in properties relating to the handling and ease of application of the binder components and/or the coating compositions themselves such as mechanical and/or storage stability, coating composition rheology (e.g., unacceptably high viscosity, etc.), unsatisfactory water retention and the like and/or in properties relating to the desirable characteristics of the coated paper made therewith such as coating hold-out, fiber coverage, coating smoothness and gloss, stiffness, printability, ink receptivity, pigment binding strength, glueability and the like. Moreover, such deficiencies are particularly pronounced in the case of the increasingly lightweight coated papers (which naturally require decreased coating weights) such as those employed largely in Europe for rotogravure printing applications.
In view of the foregoing, it is highly desirable to provide improved binder components (and improved coating compositions employing such binder) which alleviate the aforementioned deficiencies of the prior art compositions. Additionally, it is especially desirable to provide binder components and improved coating compositions which impart the desired coating properties to the ultimate coated paper product even at the relatively low coating weights applicable to (or characteristic of) coated paper for the European rotogravure printing industry (e.g., coating weights of as little as about 9 grams per square meter on a dry basis per side coated in the coated paper sheet).